The Research Of Friction Stir Lap Welding Of Al/Steel And Friction Stir Brazing Of Al/Steel Using Zn As A Filler Metal

Friction stir lap welding of Al alloys and steels were completed successfully in this article.Firstly,2mm 2A70 Al alloy and 2mm 316 stainless steel were adopted.The influence of welding parameters on the welding joints appearance was studied.Under the reasonable welding parameters,the impact of plunge depth on the appearance of cross section of joints and microstructure were discussed.Because of the tool pin inserting into stainless steel,stainless steel particles distributed in the Al side and the hooks fabricated at both sides of the joints which composed the macro-interlock structure.As is known,the macro-interlock structure would play a constructive role in improving the joints shear strength.The interlayers at the interface were discovered using the scanning electron microscope.As a well-known fact,that the thickness of the interlayers is related with the heat input.The more the heat input the thicker the interlayer.Using the X-ray diffraction,the interlayers were detected as the Fe2Al5 mostly.The mechanical properties of welding joints were tested including shear strength and micro-hardness distribution at the cross section.Under the welding parameter of n=1200r/min,v=40mm/min,d=0.3mm the highest shear strength were acquired.The micro-hardness distribution was fluctuated in different zones in Al side,as the grains size varies in different zones.In the Al side,the biggest micro-hardness was acquired at the upper side.While in the steel side,the biggest hardness was acquired at the location close to the interface.Even though the successful Al/Steel lap joints were completed,intermetallic compounds layer could not be avoided.To solve this problem,Zn was used as a filler metal in Al/Steel friction stir lap welding.The thickness of Zn filler and the tool pin inserting into the steel were set as main variable quantities in this experiment.In this study,sound Al-Zn-steel "sandwich" joint were achieved.With the tool pin inserted into zinc foil,vast zinc was stirred into aluminum fabricating Al-Zn mixing layer structure in the upper part of aluminum side.Thin steel-Zn mixing layer structure was discovered at the interface.No intermetallic compound interlayer was discovered at the interface.The lap joints with zinc foil as filler metal showed better strength than joints without filler metal.The microstructure of joints and the effect of Zn foil thickness on the joint strength were discussed.The filler metal was melted during welding and several solid solutions were detected by X-ray diffraction.The best shear strength was acquired when the filler metal was 0.3mm and the tool pin inserted into the steel with the plunge depth of 0.1mm.